Katherine made a series of long-term moves to ensure that she would be more than her older brother's regent half of the time. She became an ally of Ryan Steiner and Galen Cox's lover. She then contracted an assassin to kill her mother, which he did by means of a bomb in 3055. Katherine subtly implicated Victor and ascribed to him the motivation that he wished to become Archon-Prince. This did not play well with the few who knew the truth about Melissa's offer to abdicate, such as Morgan Kell, but much of the general public bought into it. She was also able to manipulate her brother Peter into a self-imposed exile on Zaniah, though she did not know where he disappeared to.

Katherine's next step came with the Skye Rebellion led by Ryan Steiner. Victor had Ryan assassinated, but the deeply unpopular move forced him to leave the Lyran half of the nation in the hands of Katherine, while he permanently moved his court to New Avalon. This move was especially ironic considering that Victor was raised on Tharkad and highlighted his lack of political acumen. Simultaneously, Katherine began to publicly play up her Lyran heritage and downplay her Davion half, often leaving the "Davion" of off her surname. She also took upon herself her maternal grandmother's name of "Katrina," hoping to remind people of the popular leader. This also had the effect of creating much confusion over which Katrina Steiner was being discussed. This became a quick way to tell supporters of her and her brother Victor apart. The former would call her Katrina, the latter would call her Katherine.

Archon Katherine "Katrina" Steiner-Davion in 3063 at a press conference following the events on Carver V/LibertyScreenshot from the end cinematics of the (apocryphal) computer game MechCommander 2; actress: Amanda Collins

Katherine took advantage of the news to great effect. Citing her brother's duplicity and facing an invasion, she invoked Emergency War Powers and seceded the Lyran half of the Federated Commonwealth, naming it the Lyran Alliance because she claimed that Victor had tainted "Commonwealth." She simultaneously recalled all traditionally Lyran military units to withdraw to the nation's pre-4th War boundaries, in essence ceding the worlds that Marik wanted to him. With the completion of his goal, Marik stopped his invasion. Unfortunately, things were not well in the Sarna March. Since the 4th War, Melissa Steiner insisted that Lyran units garrison the territory that was largely conquered from the Capellan Confederation since the March was, in fact, Hanse's wedding present to his wife. In the run-up to the invasion, Sun-Tzu had activated terrorist cells on the Sarna March worlds that resulted in a destabilization of planetary governments. This, coupled with the withdraw of most defending units, compounded by Marik's decision to quit the war early, resulted in a no-man's land in the center of the Inner Sphere that became known as the Chaos March.

She was publicly angered by ComStar's replacement of their own forces with Draconian units in the Lyons region.[2]

Katherine faced a challenge to her rule almost immediately from Morgan Kell, co-founder of the famed Kell Hounds and a close, personal friend of the late Archon Katrina Steiner. Soon after the formation of the Lyran Alliance, Kell all but seceded a group of worlds along the Clan Jade Falcon border and formed the Arc-Royal Defense Cordon, in essence creating his own private fief, though he publicly stated that it was to ensure the security of the border. Katherine was incensed at his actions, but allowed the public to believe he had done it with her blessing.

She soon decided that she was in need of an ally against Clan Jade Falcon besides the Kells, who she knew did not support her. She decided to leave on a diplomatic mission in person. She left Nondi Steiner and Tormano Liao in control of her fledgling nation while she went off in search of an ally in secret. While she was attempting to make contact with another Clan, forces from the reborn Clan Wolf captured the flotilla she was in. During this time she met with Wolf KhanVlad Ward and the two found an instant attraction to each other. They were then able to conclude a mutual defense pact aimed against Clan Jade Falcon.

Both of these incidents proved fortuitous as the Falcons launched an invasion in 3058, while Katherine was off on her secret mission. She returned to Tharkad to find the Falcons poised to strike at her capital, an action that would have simultaneously decapitated the Alliance and broken the Truce of Tukayyid, prompting a renewal of the Clan Invasion with the Falcons already in possession of a head-start. While the Falcons were embroiled in the fighting for Coventry, she allowed Victor to strike at the Falcons there at the head of an international task force that had originally been headed to Tukayyid for war games. She hoped that Victor would die in the fighting, showing her strange desire for Victor to destroy himself without it being directly caused by her. She was surprised and enraged when he arranged for a peaceful settlement that allowed the Falcons to retreat with their honor intact, a move that was necessitated by an invasion of their occupation zone by Clan Wolf.

During her reign as Archon, Katherine reorganized the administrative divisions of the realm, allowed "social generals" to make something of a comeback (thanks in part to her willingness to promote individuals based on political orthodoxy as opposed to military competence), cashiered many officers who opposed her ascension, and clamped down on individuals who protested against her rule.

The cooperation that was fostered at Coventry led to a broader discussion concerning ways in which the Inner Sphere forces could strike back at the Clans. Katherine offered to allow a conference to be held on Tharkad that became known as the Whitting Conference after a city on Coventry. At the first Whitting Conference, the leaders of the Inner Sphere decided to resurrect the long-dead Star League with a First Lord elected from their number every three years. Katherine attempted to gain the position of First Lord by nominating Sun-Tzu Liao, whom she believed would be voted down, leaving her as the logical compromise candidate. What she did not expect was Victor's increased political acumen. Her plan backfired when he cast the deciding vote for Sun-Tzu.

Rather than become embittered over her loss of the first First Lordship, Katherine endeavored to deprive Victor of his vote. He took the unprecedented move of leaving his little sister Yvonne as regent of the Federated Commonwealth while he led Operation Bulldog, then went off to Clan space with Operation Hunter. In his absence, Katherine was able to manipulate public opinion polls within the Commonwealth so that the people—and Yvonne herself—believed that a majority of citizens were of the opinion that Yvonne was doing a bad job. In 3060, Yvonne asked her big sister Katherine for help, which led to Yvonne abdicating her regency in favor of Katherine. The Privy Council confirmed Katherine's appointment, whereupon she began styling herself "First Princess," despite the fact the ruler of the Federated Suns had always been known as "Prince," regardless of gender. Additionally, due to her lack of military service in either the AFFC or the LAAF, Katherine was unqualified to be First Prince and technically ruled the Federated Commonwealth as regent while acting as if she were actually the First Prince of the Federated Commonwealth.[3]

One of her first actions as ruler was to dismiss Ardan Sortek as Prince's Champion and Director of the Crucis March Command and replace him with the malleable Simon Gallagher. This action was technically illegal, since only the Prince has the authority to determine the Champion, but the only action any members of the military leadership took was to resign in protest. In a series of moves that was similar to her actions in the Lyran Alliance, officers who protested her usurpation of the throne resigned. The difference in the Commonwealth was that Katherine had not spent years eroding Victor's support, so she had to deal with a much stronger and more entrenched set of Victor supporters, including Duke George Hasek, though he declined to openly challenge her. Katherine then set up another deal with Sun-Tzu Liao. In exchange for keeping her troops out of his war to reclaim the St. Ives Compact, Sun-Tzu supported Katherine in her bid to succeed him as First Lord.[3]

When Victor returned from Clan space, he found himself a leader without a nation. Having just come from some of the most brutal fighting in decades, Victor had no desire to subject the people he still saw as his to a civil war. Instead, he succeeded Anastasius Focht as ComStar's Precentor Martial in time to cast the deciding vote against Katherine at the 3061 Whitting Conference.[4]

Katherine had dealt with almost all of her siblings. Peter was in hiding, Yvonne was a wreck, and Victor had been deposed, but Katherine had yet to deal with Arthur. Arthur was supported by James Sandoval and was agitating the people of the Draconis March to remain focused on the threat from the Draconis Combine. This served Katherine's purposes because it distracted that part of the nation from her efforts to consolidate her rule, but Arthur became increasingly extreme in his speeches. Katherine gave tacit approval for Arthur's assassination. Even though fights between pro-Katherine and pro-Victor units had already erupted on worlds like Kathil and Thorin, the bombing of the building that Arthur was giving a speech from is considered the beginning of the FedCom Civil War because that action was what prompted Victor to issue a call to arms to any and all military personnel who opposed Katherine's rule.

She was closer yet to becoming First Lord at the Third Whitting Conference in 3064 on Marik. She had been nominated and there were no clear competitors when Victor, who had no political standing because he had all but resigned as Precentor Martial to lead the civil war, revealed that he had convincing evidence that Katherine had had their mother assassinated. Showing that he had again learned from her, he did not need to produce this evidence. The mere suggestion of truth was enough for her name to be withdrawn from candidacy and Christian Mansdottir was elected instead.[5]

Katherine generally allowed her military commanders free reign to prosecute the war against her brother's supporters as they saw fit. Her ace-in-the-hole was contracting the same assassin she used to kill her mother to murder Victor's lover, Omi Kurita. Omi's death in 3064 stalled Victor's task force for a full year, but, by 3067 forces under the command of Tancred Sandoval, Ardan Sortek, and finally Victor Steiner-Davion had landed on New Avalon. Katherine's death knell was sounded with the resignation of Marshal of the Armies Jackson Davion. She appointed Simon Gallagher to the post, but soon offered her surrender through Jackson on 20 April 3067.[6]

Katherine's presence within Clan Wolf and the apparent favoritism shown to her by Vlad Ward caused significant internal tension within the Clan, and resulted in Vlad Ward having to face several Trials over his conduct.[7] Ironically, in order for Katherine to come to power in the Clans, she had to shed her image as a peacemaker and become a warrior. Though she learned to pilot a 'Mech there, she was never as skilled as she was in politics.[1]. She won her Trial of Position in a Warhawk by executing an alpha strike on a much smaller mech before immediately shutting down[8]. Evidence suggests she piloted a Griffin called "Stiletto", however after the death of her benefactor Khan Ward she was transfered to a solahma unit guarding the genetic repository on Weingarten but remained close to Loremaster Katya Kerensky. Later the over-100 year old Katherine went to Terra for Paladin Victor's state funeral along with her son, though she kept a very low profile there.[9]

Katherine never married, but Alaric Wolf is her biological son. Alaric is actually a trueborn warrior in Clan Wolf, bred from Katherine and her brother Victor's genes. She somehow acquired DNA from Victor so that she could carefully raise Alaric to become her revenge against the Inner Sphere.[10]

Katherine used whatever means necessary to attain power. Rather than rely on military acumen as most of her family did, Katherine chose to build an image as a peacemaker in direct contrast to her soldier brothers, an image that she shed once she joined Clan Wolf. She wielded assassination as a political tool and was responsible for the deaths of Melissa Steiner, Omi Kurita, and Morgan Kell's wife Salome Ward, and also ordered an attempt on George Hasek II. She continually sought more and greater power and craved power for the sake of having it. Her internal monologues in the novels seem to indicate that she genuinely believed herself to be the most suited of her family to rule, although it seems likely much of this belief was self-rationalization. Katherine appears to have little actual care for anyone other than herself; even the men she professed love for, she was willing to discard or sacrifice in her drive for power. She also demonstrated distinct signs of pettiness and cruelty, regularly using her nations' resources to persecute anyone she deemed an enemy. This started with political opponents, but eventually came to include those staying neutral in the conflict between she and Victor, and even those she deemed "insufficiently loyal" (i.e., who supported her but harbored reservations regarding her policies). As she progressed on her pursuit of personal power, she began to show greater and greater signs of megalomania, and she found it difficult to maintain her image as a peacemaker.